Apparatus for electrolyzing solutions



T. L B. LYSTER AND K-. E. STUART. APPARATUS FOR ELECTROLYZING SOLUTIONS.

Patented Aug. 23, 1921.

APPLICATION FILED AUG. I3, I920.

'III gnvc'ntow UNITED, STATES PATENT orrlcs.

THOMAS L. B. LYSTER AND KENNETH E. STUART, OF NIAGARA FALLS, NEW YORK, ASSIGNORS TO HOOKER ELECTROCHEMICAL COMPANY, OF NEW YORK, N. Y., A

CORPORATION 0]! NEW YORK.

xState of New York, have invented certain new and useful Improvements in Apparatus for Electrolyzing Solutions, of whlch the following is a specification.

This invention relates to the electrolytic decomposition of solutions, and more particularly to the electrolytic decomposition" of sodium chlorid solutions in cells of the diaphragm type, a primary object of the invention being to provide an improved apparatus for supplyln to a cell, or usually to a large number of slmilar cells, a constant volume of electrolyte in unit time.

According to the invention in its preferred embodiment the electrolytic cells receive in unit time a feed of a constant volume of electrolyte, for example an aqueous solution of sodium chlorid, said electrolyte carrying salt (typically sodium chlorid) in excess of the amount normally soluble therein at the operating temperature, this excess of salt being of course present in solid phase at the moment of introduction of the electrolyte into the cell. However, our invention is not restricted to such supply of salt in solid phase, inasmuch as certain of the benefits of the invention may be secured without this procedure. p y

In the practical operation of the invention, the quantity of salt thus supplied in solid phase is nearl but not quite suiiicient to maintain the brine within the cell in a condition of complete saturation at the o crating temperature:an excess of solid sa t above the quantity required for the satura tion of the electrolyte within the cell should however be carefully avoided, asleadin to" APPARATUS FOR EEECTROLYZING SOLUTIONS.

v Specification of Letters Patent. Patented Aug. 23, 1921.

Application filed August 13, 1920. Serial No. 403,326.

fed to an electrolytic cell of the diaphragm type at the rate necessary merely to maintain percolation through the diaphragm, without an overflow, the gravity of the brine within the cell falls below that-of the feed brine by a definite amount, which is dependent upon the percentage of decomposh tion. For example in a special case, operati'og under conditions as above, the brine within the cell was found to contain on the average 254 grams of salt per liter, al though the feed brine during the same pe riod contained 285 grams per liter. The dilution within the cell was therefore approxi mately to 89% of the original concentration. The explanation of this phenomenon :1 pears to be that a certain proportion of t 6 water is left behind upon the anode side of the diaphragm. The lower gravity thereby resulting lessens the viscosity of the solution and increases the percolation'throu h the diaphragm, so that the operation of t e cell soon becomes stabilized: but the specific gravity of the solution Within the cell is permanently lowered. This is objectionable as tending not only to a higher operating voltage but to a lower concentration of cans tic solution.

It is now established that the above described dilution of the brine is a function of the quantity of caustic produced; and that for' every 100 grams of caustic delivered from the cell a proximately 180 grams of water are left ehind in the cell. If, for exam Ie, the feed brine contains 292.5 grams of so ium chlorid per liter, and the per cent. of decomposition is 50, this will amount to about 21% of the total waterdelivered to the cell with the infiowing brine. If it were possible tel-discharge this water from the anode side of the cell, the amount of water to be evaporated from the caustic would of course be correspondingly reduced: but the same object may be attained by keeping the till concentration of the liquor within the cell the brine within the cell b ing at all times kept safely below the saturation limit at the operating temperature.

For a full understanding of the invention reference is made to the accompanying drawings illustrating a typical system in accordance with our invention, it being however understood that the invention is not restricted to the particular means chosen for illustration.

In said drawings:

Figure 1 is a diagrammatic elevation, partly in section, of a typical circulating and feeding system; Fig. 1 being a plan view of the constant level tank 6;

Fig. 2 is a partial section of the same on a sligliitly enlarged scale on line 2-2 of Fig. 1; an

Figs. 3, 4, and 5 are detail sectional views of various types of feed nozzles which may be emplo ed.

Referring to Figs. 1, l and 2, 2 represents the brine storage tank; 3 the salt hopper containing fine granulated salt such as may be obtained by evaporation of the caustic liquor produced in the operation of the cells; 4 the mixing'and agitating tank; 5, 5, 5, 5 the electrolytic cells; and 6 the levelregulating tank.

The tank 4 is filled with brine from the tank 2 by opening the valve 7. 8 is a brinemetering device which may be power-driven or may take the form of a geared rotor pump of the Root blower type, as more clearly illustrated in Fig. 2. The brine flowing through this metering device turnsthe rotor 9, which drives the sprocket 10, and, through chain 11, the large sprocket 12, the latter revolvinga double-flight worm conveyer. 13 which extends throughout the length of the salt hopper at the bottom thereof. This worm feeds the dry salt forward into the Vertical open-ended pipe 14. The stream of brine from tank 2 is likewise directed into the pipe 14, where it washes the salt out of theworm as fast as it is fed forward, and carries it through the screen 15 and chute 16 into the mixing and agitating tank 4. There is therefore in the operation of this device, a fixed relation between the displacement of the brine-meter and the salt feed; so that a definite and 0011- trollable quantity of salt can be fed for a given quantity of brine. The feed ratios may be adjusted as desired by a proper choice of sprockets 10 and 12.

It will be understood that the tank 2 might be filled with water or weak brine, and by feeding the proper quantity of solid salt a saturated, under-saturated or over-saturated brine can be delivered into tank 4 at will. For the purpose of the present invention, however, brine carrying an excess of salt in solid phase will usually be required; and it is generally preferable to obtain this by filling the tank 2 with brine having a specific gravity in the neighborhood of 1.2, and adding through the hopper 3 the salt necessary to provide the required excess.

In the system chosen for illustration the tank 4 is provided with a centrifugal pump 17 driven by a motor 18. The intake 19 of the pump 17 is located close to the bottom of the tank 4, and agitators 20 are mounted upon the vertical pump shaft. The delivery pipe 21 from pump 17 is carried over the cells 5 and terminates in an elbow 22, located within the level-regulating tank 6 and directed tangentially near the bottom thereof (see Fig. 1"). 23 is the overflow inlet leading to the return pipe 24, terminating in an elbow 25 which may be directed tangentially "near the bottom of tank 4.

By means of the pump 17 and the pipes 21 and 24 a rapid circulation of the salt suspension is maintained. Thereby the mixture' in the tank 4 is kept in violent agitation and the undissolved salt is maintained in suspension during its fiow to the tank 6 and return. 26 indicates a screen which may be placed across the tank 6 between the inflow and outflow to trap any foreign matter which may find its way into the system. A 20- mesh screen has proven satisfactory for this purpose, being sufiiciently coarse to permit free passage of the fine solid salt, w iile sufiicientl fine to remove any foreign matter that would be liable to interfere with the feed of the brine to the cells or with the operation of the latter.

Above each cell 5 is provided a feedin orifice or nozzle 27. A simple form of such orifice is illustrated on an enlarged scale in Fig. 3, comprising a calibrated glass tube 28 let into the pipe 21 through a rubber sto per b means of a T 29. The stream of rine fi om the tube 28 is directed into a glass T 30, which discharges in turn into the cells, for example through lengths of rubber hose 31, connected with earthenware well-pipes 32, which extend to a point well below the liquid level. Naturally any preferred device may be used for conveying the salt suspension to the cells or distributing it therein.

The hydrostatic head upon the orifice 27 is determined by the level of the liquid in the tank 6. This may be adjusted as desired by changing the effective height of the overflow pipe 23, which can conveniently be done b screwin different lengths into the couping 33. 0 long as the level in the tank 6 is maintained constant, the orifice 28 will feed a constant quantity of brine in unit time this brine carryin therewith any desired excess of suspende salt. This rate of feed is unaffected by the level of the liquid within the cell 5 or by the gas pressure therein.

Fig. 4 illustrates a stream-1ine type of orifice, screwed flush into the pipe 21 and terminating in a succession of taperednozzles 34, screwe one upon the other, each successive nozzle being slightly smaller than the preceding one with t e result that to ether they form a uniformly tapering ori cc of whlch the aperture may be closely regulated.

The types of orifice illustrated in Figs3 and 4 are not affected by the velocity of the How in pipe 21, except as the resistance to such flow creates added static pressure. Thus if the pipe 21 be horizontal, the orifice leading to the cell farthest from the tank 6 will be under a higher static pressure than that of the cell nearest this tank, by the amount of the pressure necessary to overcome the resistance offered by the walls of the pipe 21'to the flow of the salt suspension therein. In order to equalize the static head on the several orifices, and thereby to equalize the flow through these orifices, the pipe 21 is preferably inclined toward the regulating tank 6 as illustrated in Fig. 1. It is very easy to determine experimentally the degree of inclination necessary by connecting a manome ter to each orifice, the proper inclination being obtained when all of the manometers give identical readings. f

Fig. 5 illustrates a form of orifice having a curved inlet 35 extending into the interior of the pipe 21. This type of orifice may be adjusted by turning it so as to present various angles to the direction of flow within the pipe, and is very sensitive to fluctuations in the *velocity of the brine.

By the application of the present invention to diaphragm cells having no overflow or equivalent constant-level device, an accu-. rate and wholly automatic control of the percolatlon through the diaphragm is secured,

since the level of electrolyte within the cell will automatically vary in the direction and to the precise degree necessary to secure an average percolation equivalent tothe inflow. Thereby a constant percentage of decomposi tion and a constant and high ampere efii-" ciency' is attained; while the maintenance of the saturation of the electrolyte leads to a relatively high energy efiiciency. This result in the particular svstem chosen for illus tration is dependent upon the maintenance of a constant level in the pressure-regulating in the cell, is broadly claimed in a copending application of Albert H. Hooker, Serial Number 401,391, filed Aug. 5, 1920.

We claim 1. The combination with an electrolytic cell of means for supplying electrolyte thereto; said means comprising an'external circulating system for electrolyte; a feed orifice for the cell; and means included in said circulating system for maintaining a constant head at said feed orifice.

2. The combination with an electrolytic cell of means for supplying electrolyte there to; said means comprising an external circulating system for electrolyte; a feed orifice for the cell; means included in said circulat-- ing system for maintaining a constant head at said feed orifice; and means for adjusting said feed.

3. .The combination with a plurality of electrolytic cells, of means for supplying electrolyte thereto; said means comprising an external circulating system for electrolyte; a feed orifice for each cell; and means in cluded in said circulating system for maintaining a constant and substantially uniform effective head at each of said feed orifices.

4. The combination with a plurality of electrolytic cells, of means for supplying electrolyte thereto; said means comprising an external circulating system for electrolyte; a

feed orifice for each cell; means included in electrolytic I cell, of means for supplying electrolyte there-.

to; said means comprising a circulating sys tem for electrolyte; and means for supplying falt in solid phase to the circulating electroyte.

6. The combination with an electrolytic cell, of means for supplying electrolyte thereto; said means comprising a circulating system for electrolyte; and means for continuously supplying salt in solid phase to the circul'ating electrolyte.

7. The combination with a plurality of electrolytic cells, of a common feed pipe therefor, and means for su plying electrolyte thereto at constant hea said feed pipe downwardly inclined in the direction of flow ofthe electrolyte, whereby the flow to the inthe cell, and means for maintaining a condividual cells is substantially equalized. stant head at said feed orifice.

8. The combination with an electrolytic In testimony whereof we aflix our signa- 1 cell, of means for supplying thereto electrotures. 5 lyte carrying salt in solid phase, said means comprising an agitating device for maintain- THOMAS L. B. LYSTER. ing the salt in suspension, a feed orifice for KENNETH E. STUART. 

